The copy/paste develop shortcut (Win10) Ctrl+Shift+C\V stopped working. I was online with Adobe help last night. They reset preferences and unistalled/reinstalled Lightroom Classic which didn't work. Suggested trying a different keyboard and that didn't wotk either. One thing I noticed is a small white dashed box appears when I hit the Ctrl key. Not sure if that indicates anything. Any suggestion to fix this would be gratly appreciated.
The most common cause of particular shortcuts not working is another app or utility intercepting them. Some have reported that the utility for AMD Radeon graphic chips can intercept the Ctrl+Shift+C/V shortcuts -- if you an AMD graphics chipset, start their utility and disable its use of all shortcuts.
If that doesn't help, it can be tedious to see if another app is intercepting the shortcut. The most straightforward way of testing that is to create a new temporary account, logging into it, and running LR there. If the new account doesn't have the problem, then you can use disable all hidden startup programs and services using MSConfig (google it).
I do have AMD graphics and the issue appeared right after updating the driver. Did what you suggested in AMD Raedon preferences and my copy/paste develop shortcut is back to normal. Thanks so much for you help!